SPST, SPDT, DPST, and DPDT Switches (Diagrams, Explanation)

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Single Pole Single Throw (SPST) Switch #

• 2 Pins (Terminals)
• Single Pole
  • This indicates that the switch has only one circuit control. In other words, there is only one input and one output terminal for the switch.
• Single Throw
  • This indicates that the switch has only one active position. It can either be in an “on” position where the circuit is completed, or in an “off” position where the circuit is broken.
• Typical Position Labels
  • On/Off

A SPST switch is the simplest form of switch, commonly used to turn a circuit on or off. When the switch is in the “on” position, it allows current to flow through the circuit, and when it’s in the “off” position, it interrupts the flow of current. It’s commonly represented by a simple on/off toggle switch.

Single Pull Double Throw (SPDT) Switch #

• 3 Pins (Terminals)
• Single Pole
  • This indicates that the switch has only one circuit control. In other words, there is only one input and one output terminal for the switch.
• Double Throw
  • This indicates that the switch has two active positions. It can connect the input terminal to one of two output terminals.
• Typical Position Labels
  • On/Off/On
  • On/On
  • (On)/Off/(On): The on positions are momentary and the switch doesn’t stick in those positions.

A SPDT switch allows a circuit to be connected to one of two possible paths. When the switch is in one position, it connects the input terminal to one output terminal, and when it’s in the other position, it connects the input terminal to the other output terminal. It’s commonly represented by a switch with three terminals and a lever or toggle that can be moved between two positions. SPDT switches are often used in situations where you need to select between two different options or paths in a circuit.

Double Pole Single Throw (DPST) Switch #

• 4 Pins (Terminals)
• Double Pole: This indicates that the switch has two sets of contacts (poles). Each set operates independently of the other, allowing for separate control of two circuits.
• Single Throw: This indicates that each pole of the switch has only one active position. It can either be in an “on” position where the circuit is completed, or in an “off” position where the circuit is broken.
• Typical Position Labels
  • On/Off

So, a DPST switch allows you to control two separate circuits simultaneously. Each pole of the switch can connect its input terminal to one of two output terminals. These switches are commonly used in situations where you need to control two separate circuits with a single switch, such as controlling the power to two different devices.

Double Pole Double Throw (DPDT) Switch #

• 6 Pins (Terminals)
• Double Pole
  • This indicates that the switch has two sets of contacts (poles), allowing it to control two separate circuits independently.
• Double Throw
  • This indicates that each pole of the switch can connect to one of two possible output terminals (throws), providing flexibility in directing the flow of current in each circuit.

So, a DPDT switch enables control over two separate circuits, with each pole having the ability to connect to one of two output terminals. These switches are commonly used when two circuits need to be toggled between two different states or when reversing the direction of current flow in a circuit.